Overmolding Lampshades For Car Headlights

Car lights are divided into two categories according to their functions. One category is car lighting, including headlights and fog lights, primarily used to illuminate the road at night and during rainy and foggy days, providing drivers with sufficient light to ensure driving safety; the other category is car signal lights, such as brake lights, clearance lights, and turn signals, which plays a warning and guidance role, informing others of the vehicle’s driving status. The various types of lights are shown in Figure 1. Driven by the the need for overall vehicle lightweighting, except for individual parts like bulbs and metal wires, the remaining components of car lights are almost entirely made from plastic instead of metal or glass. The headlight lampshade directly reflects the headlight’s quality and is a crucial part for the entire headlight structure. To meet the aesthetic needs of customers, headlights are evolving towards high-end, high-precision and complex. Additionally, the headlight lampshade is transitioning from single-color transparent to double colors, and is more commonly used in high-end models.
 
 
Figure 1 Locations of various types of automobile lights
 
Product design
The lampshade’s overall structure should conform to the shape and size standards of the automobile headlights, ensuring coordination with the vehicle’s appearance and function. The structural design should consider installation convenience, durability, and waterproofness to adapt to various harsh environmental conditions. The lampshade should be precisely designed according to the actual size requirements of the automobile headlights to ensure perfect installation and matching. The lampshade’s thickness and surface morphology need to be considered to achieve the desired appearance and functional performance according to design requirements. The color distribution scheme of the two-color design should be determined according to market trends and consumer preferences. The proportion and distribution of different colors need to be balanced to ensure the overall visual effect and brand recognition.
 
Overmolding headlight lampshades
The overmolding process for headlight lampshades is a complex manufacturing technology designed to achieve two different colors of plastic on the same part of the lampshades. The following are the general steps of the overmolding process:
(1) Mold design and manufacturing
First, a special mold for overmolding is manufactured according to the design requirements of the lampshade. This mold usually includes two injection ports and a rotating or moving mechanism to ensure that the two colors of plastic can be accurately injected separately and combined in the correct position during the overmolding process.
 
(2) Material preparation and pretreatment
PC (polycarbonate) and PMMA (polymethyl methacrylate) are commonly used materials for car headlight lampshades. They have good heat resistance, UV resistance, and excellent optical transparency. Choosing the right materials is crucial because they directly affect the optical effect and weather resistance of the lampshade. Determine the formula ratio of each color according to the design requirements and customer needs. In overmolding, each plastic is usually pre-mixed and granulated to ensure stable and uniform injection. High-performance plastics like PC and PMMA are very sensitive to moisture. Even small amounts of moisture can evaporate and produce bubbles during heating, affecting the product’s appearance and performance. Therefore, before overmolding, the plastic pellets usually need to be pre-dried to ensure that their moisture content is below an acceptable level.
 
(3) Overmolding machine settings
Before plastic overmolding, ensure that the barrel and mold have reached the appropriate operating temperature. Each plastic has specific melting temperature and fluidity requirements, so precisely control barrel heating temperatures and injection speeds.
 
(4) Overmolding processes
a. Injecting the first color: First, the plastic with the first color is injected from an injection port into a part of the mold. This step is usually completed in the fixed part of the mold.
b. Rotating or moving the mold: Depending on the mold design, the mold will rotate or move to allow the plastic with the second color to fill the remaining space. This ensures that the two colors are combined in the correct position to form a clear dividing line and color transition.
 
(5) Cooling and curing
Once the two colors of plastic fully fill the mold, the mold will remain for a period of time to ensure that the plastic cools and solidifies. The cooling time is usually determined by the type and thickness of the plastic.
 
(6) Removal and post-processing
When the plastic is completely cooled, open the mold and remove the finished product. The finished product may require further post-processing steps, such as trimming edges, removing support structures, and surface treatment to meet the appearance and functional requirements of the final product.
 
Through precise mold design, appropriate material selection, and strict manufacturing process control, the overmolding process can produce a car headlight lampshade with an exquisite appearance and perfect functions, meeting the automotive industry's demand for high quality and complex design.